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Chapter 7Pathways of
Cellular Respiration
Glucose Breakdown Releases Energy
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7.1 Cellular respiration is a redox reaction that requires O2
Oxidation of substrates, such as glucose, is a fundamental part of cellular respiration
NAD+ and FAD coenzymes assist in oxidation during cellular respiration carrying high-energy electrons to the electron transport chain
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Figure 7.1 Cellular respiration produces ATP
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7.2 Cellular respiration has four phases—three phases occur in mitochondria
Four phases of cellular respiration Glycolysis - an anaerobic process occurs outside
the mitochondria Preparatory (prep) reaction - in the matrix of the
mitochondria pyruvate is broken down to a 2-carbon acetyl group
Citric acid cycle - in the matrix of the mitochondria NADH and FADH2 produced
Electron Transport Chain (ETC) - NADH and FADH2 give up electrons to the chain and energy is released to produce ATP
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Figure 7.2 The four phases of complete glucose breakdown
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Carbon Dioxide and Water Are Produced During
Glucose Breakdown
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7.3 Glycolysis: Glucose breakdown begins
Glycolysis takes place outside the mitochondria and glucose is broken into two pyruvates
Inputs and outputs of glycolysis
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Figure 7.3A Glycolysis
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Figure 7.3B Substrate-level ATP synthesis
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7.4 The preparatory reaction occurs before the citric acid cycle Preparatory (prep) reaction occurs before the
citric acid cycle 3-carbon pyruvate is converted to a 2-carbon
acetyl group and CO2 is given off
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Figure 7.4 Mitochondrion structure
7.5 The citric acid cycle: Final oxidation of glucose products
Citric acid cycle - a cyclic metabolic pathway located in the matrix of mitochondria It produces a lot of the NADH and all of the FADH2
that carry electrons to the electron transport chain
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Figure 7.5 The citric acid cycle
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7.6 The electron transport chain captures much energy
Electron transport chain (ETC) located in the cristae of the mitochondria is a series of carriers that pass electrons Many of the carriers are cytochrome molecules, a
protein that has a tightly bound heme group with a central atom of iron
NADH and FADH2 are recycled to pick up more electrons to bring back to the electron transport chain
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Figure 7.6 The electron transport chain
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7.7 The cristae create an H+ gradient that drives
ATP production
Chemiosmosis As hydrogen ions flow from high to low
concentration ATP synthase synthesizes ATP from ADP + P
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Figure 7.7 Organization and function of cristae
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7.8 The ATP payoff can be calculated
Figure 7.8 Energy yield per glucose molecule 7-19
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Fermentation Is Inefficient
7.9 When oxygen is in short supply, the cell switches to fermentation
Fermentation produces a limited amount of ATP using organic molecules instead of oxygen as the final electron acceptor Benefit of Fermentation
Provide a rapid burst of ATP without oxygen
Drawback of Fermentation Creates oxygen debt Yields 2 ATP, cellular respiration yields ≥36ATP
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Figure 7.9A Fermentation
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
7.10 Fermentation helps produce numerous food products
Fermenting yeasts leaven bread and produce alcohol
Fermenting bacteria produce acids used to make yogurt, sour cream, and cheese
Soy sauce is made by adding a mold and a combination of yeasts and fermenting bacteria to soybeans and wheat
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Metabolic Pathways Cross at Particular Substrates
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7.11 Organic molecules can be broken down and synthesized as needed
Metabolic pool - substrates are entry points for degradation or synthesis of larger molecules Catabolism - reactions that break down molecules Anabolism - reactions that synthesize molecules
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Figure 7.11 The metabolic pool concept
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
7.12 Exercise burns fat
Prolonged aerobic exercise burns fat Breathing and heart rate increase during
exercise in order to supply the muscles with adequate oxygen
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Figure 7.12A Sources of fuel for exercise
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Connecting the Concepts:Chapter 7
Energy released when carbohydrates are oxidized and used to produce ATP molecules
Removal of hydrogen atoms occurs during glycolysis, the prep reaction, and the citric acid cycle NADH and FADH2 carry electrons to the electron
transport chain (ETC) to produce ATP Oxygen serves as the final acceptor of electrons, and
water is produced
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